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Adverse climate changes in Pakistan undermine the water resources and give rise to transient and permanent droughts in different parts of the country. The occurrence of drought cannot be prevented, but its detrimental impacts can be brought down by proper pre‐drought planning. Effective planning owes to using scientific and probabilistic approaches. In this paper, the interarrival time of drought for seven operational drought indices in Pakistan is modelled by using the modified distribution of convolution derived from the Bivariate Affine Linear Exponential (BALE) distribution. A new stochastic variable, interarrival time of drought, is generated from the data of drought indices from 1951 to 2016 used in Pakistan by applying the theory of runs. The proposed model identifies Palmer drought severity index (PDSI) and Reconnaissance drought index (RDI) as the most appropriate meteorological indices for the under‐study country. The quantiles of the model are computed that provide information about the interarrival time of drought and help to anticipate this phenomenon. In addition, return periods for all the seven indices are calculated to report the frequency and duration of drought over a certain period. Finally, some recommendations for the National Drought Monitoring Centre (NDMC) and Pakistan Council of Research in Water Resources (PCRWR) are stated for better future planning to avoid the adverse impacts of drought. [ABSTRACT FROM AUTHOR]

Drought seriously endangers the development of agro‐pastoral ecotone in arid and semi‐arid regions. However, drought evolution characteristics of semi‐arid sandy grassland and its drivers are not well understood in the complex climate change context. Thus, in this paper, the revised standardized precipitation evaporation indices on one‐month (SPEI‐1) and growing‐season (SPEI‐6) scale, flash drought and dry spells (DS) were calculated as drought indicators, and the temporal variabilities and meteorological drivers of drought in Horqin Sandy Land during the growing period (April–September) from 2007 to 2021 were studied. The results showed that SPEI‐1 and SPEI‐6 exhibited negative trends and periodic change. This drought aggravation was manifested in increased grades and numbers of drought months. Flash droughts can occur every month during the growing season. And its occurrence was not only positively correlated with all drought events in frequency but also synchronized in time. The increased number of DS showed an asymmetrical shift towards 7‐day‐and‐longer DS. SPEI sensitivity to precipitation (P) was noticeably higher than to atmospheric evapotranspiration demand (AED) at both monthly and growing season scales. SPEI sensitivity to AED was modulated by P amounts, which was higher during low P period. Apart from the amounts of P and AED, their temporal variability also strongly determined how they affect the drought severity. P was also the main driver for flash drought and long DS, but AED with larger amount and higher variability is the reason for their aggravation. Our results demonstrate the complexity of drought intensification in semi‐arid sandy grasslands and highlight the important role of AED anomalies in it. [ABSTRACT FROM AUTHOR]

This paper analyses extreme meteorological droughts in the territory of the Pannonian Basin in central and southeastern Europe. Droughts are treated from an agricultural perspective as periods of consecutive days with very little or no rainfall at all. By using data from the historical period 1981–2010, time intervals longer than 20 days with less than 3 mm per day during the growing season April–September are examined to determine theoretical and empirical distributions of their number and durations. Related discrete stochastic process of extremes is analysed by the Zelenhasic–Todorovic (ZT) method, successfully applied in hydrology and meteorology (e.g., peak flows, low flows, meteorological droughts, etc.). The method is applied to 52 locations across Pannonia Basin. At each location, the Poisson distribution is determined for the number of droughts, exponential distribution for the duration of droughts, and double exponential distribution for the duration of the (annually) longest droughts. To validate the quality of modelling and the results obtained, standard statistical goodness of fit tests are used. Historical data from the period 1981–2010 indicate that the central and northern part of Hungary and the entire territory of Vojvodina Province in the north of Serbia experienced the longest droughts, on average 55–60 days. In statistical terms, across Pannonia Basin once in 100 years drought may occur with an average duration of 56 days. Theoretically longest 100‐year droughts could be expected in the northern part of Hungary (up to 70 days), the eastern part of Romania (up to 68 days), and Serbia (up to 69 days). The 2‐year droughts are on the average duration of 3 weeks. Generated maps of the longest droughts in the basin may help to reduce agricultural risks due to global warming and other negative impacts of climate change. [ABSTRACT FROM AUTHOR]

In this paper, we report on the frequency of false onsets of wet season rainfall in the case of the Northern Australian wet season and investigate the role of large‐scale tropical climate processes such as the El Niño–Southern Oscillation, Indian Ocean Dipole (IOD) and Madden–Julian Oscillation. A false onset occurs when a wet season rainfall onset criterion is met, but follow‐up rainfall is not received for weeks or months later. Our analysis of wet season rainfall data from 1950 through 2020 shows a false onset occurs, on average, between 20 and 30% of wet seasons across all of northern Australia. This increases at a regional and local level such as at Darwin, the Northern Territory (NT), and parts of Queensland's north coast to over 50%. Seasonal climate influences, such as a La Niña pattern and a negative IOD that typically expedite the wet season rainfall onset, also increase the likelihood of a false onset over northern Australia. Our analysis also finds that periods of false onsets can sometimes, but not always, coincide with periods of rapid soil moisture depletion. The false rainfall onsets that develop into flash drought can be potentially disruptive and costly and are of potential significance for agriculture and fire management in northern Australia, and in other monsoonal climates that also typically experience a slow build‐up to the seasonal monsoon. In conclusion, effective rainfall indicates that many seasons experience 'false onsets' with dry conditions after early rainfall. We propose that false onsets are a physical characteristic of the climate of northern Australia which occurs with relatively high frequency. In addition, these false onsets may sometimes co‐occur with a flash drought. [ABSTRACT FROM AUTHOR]

Drought events occur worldwide and possibly incur severe consequences. Trying to understand and characterize drought events is of considerable importance in order to improve the preparedness for coping with future events. In this paper, we present a methodology that allows for the delineation of drought events by exploiting their spatiotemporal nature. To that end, we apply operators borrowed from mathematical morphology to represent drought events as connected components in space and time. As an illustration, we identify drought events on the basis of a 35‐year data set of daily soil moisture values covering mainland Australia. We then extract characteristics reflecting the affected area, duration and intensity from the proposed representation of a drought event in order to illustrate the impact of tuning parameters in the methodology presented. Yet, this paper we refrain from comparing with other drought delineation methods. [ABSTRACT FROM AUTHOR]

Amazon tropical forests and the semiarid Northeast Brazil (NEB) region have registered very severe droughts during the last two decades, with a frequency that may have exceeded natural climate variability. Severe droughts impact the physiological response of Amazon forests, decreasing the availability to absorb atmospheric CO2, as well as biodiversity and increasing risk of fires. Droughts on this region also affect population by isolating them due to anomalous low river levels. Impacts of droughts over NEB region are related to water and energy security and subsistence agriculture. Most drought episodes over Amazonia and NEB are associated with El Niño (EN) events, anomalous warming over the Tropical North Atlantic (TNA), and even an overlapping among them. However, not all the dry episodes showed a large‐scale pattern linked to a canonical EN event or warm TNA episodes. For instance, dry episodes linked to EN events present distinct spatial patterns of precipitation anomalies depending on EN type (Central‐Pacific vs. Eastern‐Pacific EN), and NEB region experienced a severe drought in 2012 that is not attributed to EN or warm TNA events. Even in the case of the strong EN in 2015/16, some regional impacts have not been explained by EN contribution. This paper discusses the effects of CP and EP EN events, and the role of warm TNA events on tropical Walker and Hadley circulation leading to drought over Amazonia and NEB regions. [ABSTRACT FROM AUTHOR]

This paper analyses extreme rainless periods for the territory of Serbia in southeast Europe. Treated as meteorological droughts from an agriculture perspective, the number of rainless periods longer than 20 days as well as their distributions is examined for the growing season (April–September) using data from a period of 50 years. The related stochastic process is modelled via the Zelenhasic–Todorovic (ZT) method for 20 evenly distributed locations across Serbia and important results are mapped in a geographic information system (GIS) environment. The principal components of the process are the number of rainless periods following a Poisson distribution, the theoretical exponential distribution of all droughts' duration and the theoretical double exponential distribution of the (yearly) longest drought's duration. These components are significant for agriculture under climate change because frequent and long‐lasting periods without or with very small amounts of rainfall (e.g., 3 mm·m−2·day−1) have a negative impact on crop production and require additional agricultural measures. This study shows that rainless periods long up to 45 days can be expected every 5 years. Extremely long droughts up to 75 days can be expected every 100 years. The saturation effect, visible if the distribution functions of the longest rainless periods are analysed for different return periods (100, 50, 20, 10, 5 and 2 years) at different locations in Serbia, illustrates that droughts of longer than approximately 55 days may occur every 50 years, while shorter droughts (30–33 days) may be expected every second year. Through quantifying the spatial and temporal distribution of rainless periods across Serbia, this work demonstrates that periods without rain are at least equally important as periods with rain. As both are aspects of a unique climate variability process, they influence agriculture and other socio‐economic sectors and have major impacts on the reliability, resilience and vulnerability of production systems, industries and services. [ABSTRACT FROM AUTHOR]

Future precipitation changes impact the availability of water resources and related flood and drought events. Recent studies have focused on the variations in precipitation based on the Representative Concentration Pathways scenarios, which do not reflect the current mitigation commitments of the Paris Agreement to stabilize the global mean temperature below the 2.0°C threshold. This paper analyzes the Asian precipitation response to emissions scenarios from warming. This response is a result of the Intended Nationally Determined Contributions (INDC) pledges (as of August 2018), which would satisfy the Paris Agreement target over the next few decades. Our results demonstrate that by the end of 21st century, mean precipitation in Asia will increase by 12.9% (11.7–14.7%) for a delayed action (No‐policy) scenario, 8.0% (6.7–8.8%) for a continued mitigation action (continued INDC‐pledge) scenario, and 2.4% (1.9–3.5%) and 4.4% (3.7–5.4%) for scenarios that stabilize the global mean temperature at the 1.5 and 2.0°C levels, respectively. The spatial heterogeneity of precipitation changes, however, reflects the complexity of precipitation responses in future climate projections. Furthermore, heavy rainfall events will become stronger as warming increases; however, the trend of dry spell events varies depending on the region. Considering the impacts of precipitation‐related extremes, we determined that the projected population exposure to heavy rainfall and dry spell events will significantly increase in most Asian regions. Limiting warming to lower levels (such as 1.5 or 2.0°C) would reduce the population exposure to heavy rainfall, thereby avoiding impacts associated with precipitation extremes. These results contribute to an improved understanding of the risks related to future climate extremes. Such information is crucial for planning mitigation and adaptation activities in Asia, which is home to nearly 60% of the global population. [ABSTRACT FROM AUTHOR]

Brazilian Cerrado biome is the largest and richest tropical savanna in the world. In order to understand the effects of climate changes on the hydrology of the Cerrado basins, this paper investigates the hydrological impacts of climate change throughout the 21st century under different emissions scenarios on the streamflow and on the droughts in the Sono, Manuel Alves da Natividade and Palma basins, located in the Brazilian Cerrado. For this purpose, the SWAT hydrological model driven by the downscaling of the HadGEM2‐ES and MIROC5 global climate models associated with RCP4.5 and RCP8.5 scenarios were used in three time slices (2011–2040, 2041–2070 and 2071–2099). The Standardized Precipitation Index (SPI) and the Standardized Streamflow Index (SSFI) were used to characterize droughts. In general, the results showed that the duration, intensity and frequency of the meteorological and hydrological droughts are expected to increase during the future periods. However, the hydrological droughts are projected to be larger than the meteorological droughts. Reductions in the streamflow are indicated in all future time slices and under both RCPs, especially, during dry periods, which may cause negative impacts in the ecological functions of the Cerrado biome, risk for reduction of the recharge of aquifers and risk for the electric energy production in northern Brazil. [ABSTRACT FROM AUTHOR]

Drought occurs more frequently in the context of climate change and threatens water security worldwide. An appropriate fitting distribution is crucial for accurately identifying drought using drought indices. Here, seven two‐parameter distributions (Gamma, Gumbel, Logistic, Log–Logistic, Log‐normal, Normal, and Weibull) and four distributions (general logistic, generalized extreme value, Normal, and Pearson Type III) are applied to calculate the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI), respectively, to choose the most appropriate fit for the 541 stations in China. The results show that, in most cases, Gamma and general logistic were the best distributions for SPI and SPEI, respectively. Nevertheless, we noted that Pearson Type III and generalized extreme value also fit the SPEI series well, indicating the importance of distribution fitting assessment for various regions. The annual and seasonal drought evolutions across China were clarified, with drought decreasing significantly in western Northwest China (annually and each season), northern North China (spring and winter), the Tibetan Plateau (spring), and the lower reaches of the Yangtze River (winter) and increasing mainly in South China (spring) and western South China (summer and autumn). The intensity, duration and severity of light, moderate, and severe drought were also detected; the results suggest that drought in China is mainly concentrated around the changes in light and moderate drought. Additionally, we assessed the sensitivity of drought evolution to various meteorological variables. The most sensitive variable in South China, North China and the Tibetan Plateau is precipitation, followed by wind speed, temperature, relative humidity, and sunshine duration; in Northwest China, the order is wind speed, precipitation, temperature, relative humidity, and sunshine duration. Furthermore, the correlation results also indicate that the drought evolution is affected by the multivariate ENSO index, while the influencing characteristics are different in various seasons and regions. The results in this paper contribute to drought mitigation and the effective utilization of water resources in China. [ABSTRACT FROM AUTHOR]

Model‐based sensitivity experiments are a widely used method for studying climate change attributions. In traditional climate sensitivity studies, "climate drift" occurs because of the accumulation of model errors during long‐term integrations, both in "actual" and "hypothetical" states. A more accurate piecewise‐integration method is used to reduce the model errors, dividing the continuous simulation into a series of sequential short‐term simulations. The model fields are updated at the end of each subinterval with analysis data for the "actual" state run, and with the sum of the analysis data and the difference between "hypothetical" and "actual" states for the "hypothetical" state run. This paper conducts sensitivity experiments with the continuous‐integration method and the piecewise‐integration method to evaluate the impacts of the central and eastern Pacific Ocean sea surface temperature anomalies (SSTAs) on the severe drought that occurred in southwestern China (SWC) in the winter of 2009/2010. The results show the following. (a) Model errors produced by the piecewise‐integration method for the actual state simulation are significantly less than those produced by the continuous‐integration method. (b) The intensity of the drought is significantly overestimated in continuous‐integration experiments. However, the drought can be accurately simulated in its spatial distribution and intensity via the piecewise‐integration method. Thus, climate sensitivity to changes in external forcing can be studied with greater credibility. (c) The warm central Pacific Ocean SSTAs may be the main cause of the drought over SWC. Adequate precipitation occurred over SWC when the centre of the SSTAs shifted to the east. (d) Warm SSTAs over the central Pacific Ocean influenced precipitation over SWC by weakening the water vapour transport branch from South China Sea to SWC. With a deficit of water vapour, the pronounced subsidence and warm temperatures were the main dynamic and thermodynamic factors that caused and maintained the drought. Model‐based sensitivity experiment is a method of studying climate change attributions. In traditional climate sensitivity studies, "climate drift" occurs both in "actual" and "hypothetical" states. Therefore, the scientific value of climate sensitivity experiments is questioned. In this study, piecewise‐integration method (shown in the figure) is used to significantly reduce model errors caused by inaccuracies of analysis fields, to improve the accuracies of climate sensitivity simulations and to evaluate the impacts of the Pacific Ocean SSTAs on a drought. [ABSTRACT FROM AUTHOR]

The Sahel region is known for the multi‐decadal occurrence of severe drought that commenced in the late 1960s. A still open question is whether or not the region's rainfall has returned to “normal.” This paper provides a compelling answer to that question by examining the longest and most comprehensive gauge series for the region ever published. It extends from 1854 to 2014 and is based on 602 gauge records. A comparative series for the Guinea Coast region to the south is also presented, as the two regions collectively provide insight into the long‐term variability of the West African monsoon. In contrast to many previous studies, here the question of recovery and regime change is not restricted to the core of the Sahelian rainy season (July–September), but is separately discussed also for the coastal phase (April–May), transition phase (June), Sahelian phase (July–September) and the second transition phase (October–November) of the West African monsoon. These analyses suggest that full recovery from the droughts of the 1970s and 1980s has not occurred that a major change in the rainfall regime occurred around 1968 and that since that time large‐scale teleconnections have also changed markedly. The shift post‐1968 is evident in all phases of the monsoon except the coastal phase, in which a change to drier conditions occurred a decade later. Overall, recovery has been greater in the east than in the west, creating a change in the climatological east–west rainfall gradient. The drier post‐1968 conditions appear to be associated with a general weakening of the intensity of the West African monsoon and only a small southwards displacement of the rainfall maximum. These changes have strong implications for the future of this region and for seasonal prediction. [ABSTRACT FROM AUTHOR]

ABSTRACT: Soil moisture affects hydro‐climate processes by altering water and energy exchanges between land surface and atmosphere. Understanding of the predictability of soil moisture is not only important for a skillful forecasting of seasonal hydro‐climate, but also for agricultural drought early warning. This paper assesses seasonal forecast skill and potential predictability of soil moisture directly produced by climate models, and investigates an optimal combination of different models over China. A set of 29‐year hindcasts for soil moisture from six North American Multi‐model Ensemble (NMME) models are verified against ERA Interim reanalysis. Results show that soil moisture predictability, which is defined by anomaly correlation under a perfect model assumption, is higher than forecast skill in all models, suggesting that soil moisture prediction may have a room for improvement. Except the CESM model, NMME climate forecast models with higher predictability also have higher forecast skill, where predictability is positively correlated with forecast skill with p < 0.01 across different lead times. Soil moisture forecast skill from NMME simple arithmetic mean is higher than any individual models, and the skill is further improved through an optimization of model weights with a cross validation procedure. As compared with simple ensemble mean, the optimized superensemble mean reduces root mean squared error by 19 and 7% for seasonal mean soil moisture forecast during winter and summer seasons, respectively, and increases correlation by about 10%. This study suggests that soil moisture forecasts directly produced by climate models, when combined appropriately, can provide useful information for climate service. [ABSTRACT FROM AUTHOR]

ABSTRACT Water scarcity is a critical issue in Iberia but few studies have investigated future drought over the region. The few that do are continental or global studies and do not report the range of possible future projections. In this paper, historical drought and future projections of drought were examined, using observed and downscaled rainfall data from climate models, for the main Iberian international basins (Douro, Tagus and Guadiana). Two drought indices were used, the standardized precipitation index ( SPI) and the drought severity index ( DSI). However, problems were found in the distribution fitting required for the calculation of SPI which render this index inadequate for assessing droughts in Iberia. The skill of CMIP5 climate models in representing historical drought for the Douro, Tagus and Guadiana is very variable with some not showing enough persistence of dry conditions, and others simulating droughts that are too long and too severe. Nevertheless, the observed range of drought conditions for these basins was encompassed by the ensemble members. Furthermore, we found no relationship between performance in simulating mean large-scale circulation and model ability to reproduce the historical drought characteristics for the region. All models project an intensification of drought conditions for the three basins. However, some only project small increases, while most project extreme multi-year droughts by the end of the century. We found that climate model future projections are neither related to their performance in simulating historical drought nor to their large-scale circulation patterns. This result emphasises the need for climate change impact studies to take into account the whole range of climate model projections in order to provide the best information for robust adaptation. Choosing one or a subset of climate models based on historical performance would not lead to a credible and justified reduction in uncertainty. [ABSTRACT FROM AUTHOR]

After the frequent and long drought episodes of the 1980s, a plethora of case studies have shown that West Africa remains a hot spot in the continent where despite its numerous water resources, extreme rainfall variability remains a profound challenge to the availability of freshwater for agriculture and ecosystem services. In this paper, we assess the recent flux in water availability over West Africa by investigating variations in net-precipitation (i.e. the maximum available freshwater flux) using wavelet analysis. Net-precipitation was obtained as a residual of the atmospheric water balance, and its variability compared to precipitation, temperature, evaporation, soil moisture and normalized difference vegetation index using wavelet power transforms and coherence analysis. Results from the study indicate that the variance in water flux over the region has been progressively reducing, suggesting a relative reduction in extreme hydrological conditions. Also, the wavelet coherence analysis revealed that the observed decreasing rate of available freshwater is highly coupled to a low frequency modulating El-Nino activity that induced lower changes in rainfall variance, as well as higher evaporation variance. Spatial trends in the annual-scaled average wavelet power indicated that the south-western parts of the region experienced the most reduction in rainfall flux. The highest deficit in net-precipitation flux was found in the dry sub-humid climatic zone, which is drained by major regional rivers, including the Niger and Volta. Considering the long-term variability in freshwater (i.e. from 1979 to 2010), we found the 1980s to be the driest decade and the 1990s being its recovery period, while the 2000s proved to be a considerably dry decade, suggesting a strong multi-decadal variability. [ABSTRACT FROM AUTHOR]

ABSTRACT After the frequent and long drought episodes of the 1980s, a plethora of case studies have shown that West Africa remains a hot spot in the continent where despite its numerous water resources, extreme rainfall variability remains a profound challenge to the availability of freshwater for agriculture and ecosystem services. In this paper, we assess the recent flux in water availability over West Africa by investigating variations in net-precipitation (i.e. the maximum available freshwater flux) using wavelet analysis. Net-precipitation was obtained as a residual of the atmospheric water balance, and its variability compared to precipitation, temperature, evaporation, soil moisture and normalized difference vegetation index using wavelet power transforms and coherence analysis. Results from the study indicate that the variance in water flux over the region has been progressively reducing, suggesting a relative reduction in extreme hydrological conditions. Also, the wavelet coherence analysis revealed that the observed decreasing rate of available freshwater is highly coupled to a low frequency modulating El-Niño activity that induced lower changes in rainfall variance, as well as higher evaporation variance. Spatial trends in the annual-scaled average wavelet power indicated that the south-western parts of the region experienced the most reduction in rainfall flux. The highest deficit in net-precipitation flux was found in the dry sub-humid climatic zone, which is drained by major regional rivers, including the Niger and Volta. Considering the long-term variability in freshwater (i.e. from 1979 to 2010), we found the 1980s to be the driest decade and the 1990s being its recovery period, while the 2000s proved to be a considerably dry decade, suggesting a strong multi-decadal variability. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper investigates the spatial and temporal properties of persistent meteorological droughts using the homogeneous Island of Ireland Precipitation ( IIP) network. Relative to a 1961-1990 baseline period it is shown that the longest observed run of below average precipitation since the 1850s lasted up to 5 years (10 half-year seasons) at sites in southeast and east Ireland, or 3 years across the network as a whole. Dry spell and wet spell length distributions were represented by a first-order Markov model which yields realistic runs of below average rainfall for individual sites and IIP series. This model shows that there is relatively high likelihood ( p = 0.125) of a 5-year dry spell at Dublin, and that near unbroken dry runs of 10 years or more are conceivable. We suggest that the IIP network and attendant rainfall deficit modelling provide credible data for stress testing water supply and drought plans under extreme conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper reviews recent progress in the study and understanding of extreme seasonal events in the Amazon region, focusing on drought and floods. The review includes a history of droughts and floods in the past, in the present and some discussions on future extremes in the context of climate change and its impacts on the Amazon region. Several extreme hydrological events, some of them characterized as 'once in a century', have been reported in the Amazon region during the last decade. While abundant rainfall in various sectors of the basin has determined extreme floods along the river's main stem in 1953, 1989, 1999, 2009, 2012-2015, deficient rainfall in 1912, 1926, 1963, 1980, 1983, 1995, 1997, 1998, 2005 and 2010 has caused anomalously low river levels, and an increase in the risk and number of fires in the region, with consequences for humans. This is consistent with changes in the variability of the hydrometeorology of the basin and suggests that extreme hydrological events have been more frequent in the last two decades. Some of these intense/reduced rainfalls and subsequent floods/droughts were associated (but not exclusively) with La Niña/El Niño events. In addition, moisture transport anomalies from the tropical Atlantic into Amazonia, and from northern to southern Amazonia alter the water cycle in the region year-to-year. We also assess the impacts of such extremes on natural and human systems in the region, considering ecological, economic and societal impacts in urban and rural areas, particularly during the recent decades. In the context of the future climate change, studies show a large range of uncertainty, but suggest that drought might intensify through the 21st century. [ABSTRACT FROM AUTHOR]

Various studies have been performed on drought hazard assessment at the national or regional scales, but few studies to date at the global scale, especially on global agriculture. In this paper, we utilized an agricultural drought hazard index (DHI), based on both drought severity and drought occurrence rate, derived from 3-month scale Standardized Precipitation Index (SPI) and the phenology data of main crops (rice, maize, wheat, barley, sorghum and soybean) to assess the agricultural drought hazard grades of the world during 1980-2008. The results indicated that area percentages of high and very high agricultural drought hazard zones were approximately 23.57 and 27.19% of the total agricultural area in the world. Moreover, those zones mostly were distributed in central United States, southeastern South America, most of Europe, southwestern Russia, both southern Congo and Nigeria, east-central and southwest China, Southeast Asia and eastern Australia, and most of those areas were also located in semi-humid or humid climate zones. In addition, some regions above were also found to be the very high agricultural drought hazard zones for the main crops: East-central and southwest China for wheat, maize, rice and soybean; Europe for wheat, maize and barley; Southeast Asia for rice; both central United States and southeastern South America for wheat, maize, soybean and sorghum. [ABSTRACT FROM AUTHOR]

ABSTRACT Understanding the conditions of droughts are imperative for many purposes especially in planning and agricultural fields. In this paper an attempt is made to analyse rainfall distribution during droughts associated with El Niño and non-El Niño events using India Meteorological Department (IMD) daily rainfall data set having a spatial resolution of 0.25° latitude × 0.25° longitude grid. Patterns of rainfall during drought years which are not associated with El Niño have below normal rainfall over most places of Indian subcontinent, except peninsular India and eastern region. Most of the drought conditions of the Indian summer monsoon rainfall are associated with El Niño (13 of the 18 years) indicating that about 72% of the drought years are associated with the influence of Pacific Ocean. North India and most of the central Indian regions are under below normal rainfall especially over west coastal stations there the severity of drought is strong. The drought that are associated with El Nino are much intense in most parts of the subcontinent, it severely affected the entire west coastal belts, monsoon zone and eastern regions than the droughts associated with non-El Nino years. The spatial patterns of rainfall during flood years associated with La Niña events and drought years associated with El Niño reveal that the spatial structure of rainfall is highly non-linear. These results are also verified using APHRODITE rainfall data. Over central India and Western Ghats (WGs), the drought associated with El Niño gives clear indication of droughts from the early June onward, however, in the case of non-El Niño-related droughts, the indication of drought can be seen only after the first week of July. The study suggests that droughts associated with El Niño events bring severe drought conditions over WG region. However, over central India, there is no considerable difference in cumulative rainfall associated with the two types of droughts. The intraseasonal properties of rainfall are prominently different from non-El Niño to El Niño droughts. During El Niño droughts, the variance of rainfall in both the central Indian and WG regions is weaker than the droughts that are not associated with El Niño. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, we examine the relationship between short- and long-term effects of precipitation deficits, integrated in a drought index called 'Joint Deficit Index ( JDI)', and tree-ring growth of oak trees ( Quercus infectoria) in the Javan-Roud region, Kermanshah province (Iran). Precipitation data from regional climate stations cover the period 1968-2008, and the tree-ring width chronology span over the period 1818-2008. This chronology is highly correlated with the JDI (January-September) series for the instrumental period ( P < 0.01). Therefore, the regional JDI was reconstructed using a simple linear regression model which accounts for 40% of JDI (January-September) variances over the instrumental period. Reconstructed drought periods persisted on average for 2 years, and some severe drought lasted for 3-4 years. However, one 7-year drought was reconstructed over the period 1923-1929. The most severe droughts occurred in the periods 1960-1963 and 1999-2001. While the reconstructed JDIs have no significant correlation with the North Atlantic Oscillation, a significant negative correlation was observed with the Southern Oscillation Index in November and December of pre growth during the common period from 1877 to 2008. An appropriate agreement was found between our reconstruction and historical famines in Iran and also reconstructed results from neighbouring countries in the east (China) and west (Turkey and other countries around the Mediterranean Sea), particularly for the most severe droughts. The highest agreement was achieved with regions in the pathway of westerly storm tracks travelling via the Mediterranean region into Iran. [ABSTRACT FROM AUTHOR]